During fabrication and after a period of use it is desirable to test the interior parts in such items as heat exchangers and once such parts have been enclosed within their shell access to them is very difficult. This difficulty may be increased in the case where the heat exchangers have been used in nuclear power installations by the fact that, after a period of use, there may be some radioactive activity within the shell.
There are often small blanked-off hand-holes in the shell and these represent the only convenient access to the shell interior. Accordingly a testing apparatus must be capable of being passed through such a hand-hole.
One form of testing is to move a probe such as an ultra sonic or eddy current probe over the surface of a part to be tested to locate flaws.